"I believe that the strike by the U.S. and the alliance will take place soon -- very soon," Abdullah Abdullah told a news conference in Afghanistan. "An attack is imminent."

He said the expected strikes will target Taliban camps.

"Our helicopters are not flying for the next few days. We have closed the airspace since yesterday afternoon."

Abdullah's prediction, and several reports of increased military activity throughout the region Sunday, came as the Taliban floated an offer to try suspected terrorist Osama bin Laden in Afghanistan under Shariah, or Islamic law, for his alleged role in the September 11 attacks on New York and Washington.

The Taliban ambassador to Pakistan -- the only nation that recognizes the Taliban regime -- said Sunday that the Taliban would detain bin Laden if the United States made a formal request and provided evidence that justifies a trial.

The United States refused to consider the new offer. President Bush said Saturday that time was running out for the Taliban to hand over bin Laden and shut down all al Qaeda terror network operations.

"The president made clear his demands," an administration official said. "Those demands are not subject to negotiation and it is time for the Taliban to act now."

Tension, troop movements in the north

The Taliban are moving a significant number of troops toward Mazar-e-Sharif, a Taliban stronghold near Afghanistan's border with Uzbekistan, CNN has learned.

U.S. troops arrived at the weekend in Uzbekistan, a former Soviet republic. Some 1,000 light infantry troops from the U.S. Army's 10th Mountain Division, of Fort Drum, New York, were to be deployed.

Witnesses said activity around the Uzbek air base at Khanabad, in the southeast of the country, has increased dramatically in recent days, with large planes and military helicopters flying in and out.

On Sunday, a senior Pentagon official confirmed the increased U.S. military activity at a base in southern Uzbekistan.

Uzbek President Islam Karimov announced Friday that he was allowing the United States to use an Uzbek air base, but only for humanitarian missions.

He did not say which air base would be involved, but Khanabad is just 50 kilometers north of the Afghan border.

The agreement on use of the air base came after last week's whirlwind tour of the Middle East and South Asia by U.S. Defense Secretary Donald Rumsfeld, during which he held talks with Karimov on Uzbekistan's role in the coalition against international terrorism.

A Taliban official said on a radio broadcast in Afghanistan that the forces being moved to the Uzbek border were prepared to fight to the last in order to repel any ground invasion.

The Taliban claim to have between 40,000 and 60,000 soldiers ready to fight. Saturday, Taliban officials threatened to attack Uzbekistan if it allowed a U.S. strike against Afghanistan to be launched from Uzbek territory.

As troops amassed on both sides of the Afghan-Uzbek border, Taliban's supreme religious leader warned the U.S. not to use them as scapegoats for the attacks on New York and Washington.

A translated statement from Mullah Mohammed Omar reads, in part: "Those who have perpetrated the attacks in the United States have left no traces behind them.

"If the United States thinks that the hijackers were the real culprits, then they have been killed... no one will commit suicide on the orders of another or for the aims and interests of others."

He says Aybek, provincial capital of Samangan province, and five villages in the province have been taken. The move brings the alliance closer to Mazar-e-Sharif. Aybek is about 80 kilometers southeast of Mazar-e-Sharif.

Also, the Northern Alliance claims to have seized 10 villages in the province of Ghowr, about 200 kilometers southwest of Mazar-e-Sharif. The alliance claims to have surrounded Chaghcharan, the provincial capital, and to have seized 10 villages. The town is strategically important because it has an airport and is on a supply route to Mazar-e-Sharif.

The alliance claims the defections of 60 Taliban fighters and the capture of 100 others.